I propose to investigate the control of gene expression during meiosis and spore formation (collectively termed sporulation) in baker's yeast (Saccharomyces cerevisiae), a simple, model eucaryote. Sporulation is under the control of a large number of genes most of which appear to be required for both vegetative growth and sporulation, while a few appear to be required exclusively for sporulation. The aim of the proposed research is to determine if a transcriptional program involving sporulation specific genes is required during meiosis and spore development in yeast. The experimental plan is to show the existence of and isolate the sequences which are differentially expressed during sporulation and vegetative growth. Three approaches will be taken to isolate recombinant DNA clones containing these sequences: 1) use differential plaque filter hybridization to screen a library of recombinant yeast: lamlba DNA bacteriophages for sequences that hybridize preferentially to RNA sporulating cells; 2) develop a new physical method to enrich for mRNA which is specifically found during sproulation and to amplify these sequences as cDNA clones; 3) screen a clone bank of "Y" vectors containing random yeast DNA inserts for their ability to transform and complement yeast mutants which cannot sporulate. Furthermore, to establish that the sequences isolated by the first two approaches contain DNA coding for functions essential for sporulation, this cloned DNA will be used to induce sproulation defective mutants by transformation. Finally, we will begin a study of the cloned sequences to characterize the temporal patterns of transcription during sporulation. Our ultimate aim is to understand the genetic controls involved in meiotic differentiation in yeast; information which should be releveant to the process of meiosis in higher organisms.